The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Memory devices include an array of memory cells that store information. Memory devices may be volatile or non-volatile. Non-volatile memory devices can retain stored information even when not powered, whereas volatile memory devices typically do not retain stored information when not powered. Examples of memory devices include read-only memory (ROM), random access memory (RAM) and flash memory.
FIG. 1 illustrates a conventional memory system 100. The memory system 100 includes an array 102 of memory cells 104-1,1, 104-1,2 . . . , and 104-M,N (referred to herein as memory cells 104), a word line decoder 106, word line drivers 108, a bit line decoder 109, and sense amplifiers 110. The word line decoder 106 may select one of M rows of memory cells 104 for reading and writing operations via word lines 112-1, 112-2, . . . , and 112-M (referred to herein as word lines 112). The word line drivers 108 may apply a voltage to the selected word line 112 to activate the memory cells 104 in communication with the selected word line 112. The sense amplifiers 110 may detect the presence or absence of data stored in the memory cells 104 via global bit lines 114-1, 114-2, . . . , and 114-N (referred to herein as global bit lines 114). The bit line decoder 109 may select one of N columns of memory cells 104 for reading and writing operations via the global bit lines 114.
Each of the memory cells 104 may include diodes 105-1,1, 105-1,2 . . . , and 105-M,N (referred to herein as diodes 105) and a data storage element 107-1,1, . . . , and 107-M,N (referred to herein as data storage element 107). Alternatively, each of the memory cells 104 may include transistors (not shown) and a data storage element 107. Each diode 105 may communicate with a corresponding word line 112 and a corresponding data storage element 107. Other configurations are possible for the memory cells 104.
Referring now to FIGS. 2A-2B, the array 102 of memory cells 104 may be arranged in blocks 116-1, 116-2, . . . , and 116-Q (referred to herein as blocks 116). A block 116 may include local word lines 118-1,1, 118-2,1, . . . , and 118-V,Q (referred to herein as local word lines 118) and local bit lines 120-1,1,1, 120-2,1,1, . . . , and 120-W,L,Q (referred to herein as local bit lines 120). Memory cells 104 may be formed at the intersection of the local word lines 118 and the local bit lines 120. The local word lines 118 may communicate with respective word line decoders 106-1, 106-2, . . . , and 106-Q (referred to herein as word line decoders 106) and word line drivers 108-1, 108-2, . . . , and 108-Q (referred to herein as word line drivers 108).
The local bit lines 120 may be arranged in groups. A group of local bit lines 120 may communicate with multiplexers 122-1,1, 122-2,1, . . . , and 122-L,Q (referred to herein as multiplexers 122). Each multiplexer 122 may include a control input 123 that selectively controls which input to the multiplexer will be output from the multiplexer. A read/write (R/W) control module (not shown) may provide the control inputs. A block 116 may communicate with L multiplexers 122, which may select respective local bit lines 120 for reading and writing operations. The multiplexers 122 may communicate with respective global bit lines 114. The global bit lines 114 may communicate with each block 116 in the memory array 102. Bit line decoders 109 and sense amplifiers 110 (shown in FIG. 1) may communicate with the global bit lines 114.
The memory system 100 may include a read/write (R/W) control module (mentioned above). The R/W control module may control R/W operations of the memory cells 104 via the word line decoder 106, the word line drivers 108, the bit line decoder 109, and the sense amplifiers 110. The R/W control module may execute a read cycle to access data stored in one or more data storage elements 107 of the memory cells 104. The R/W control module may also execute a write cycle to store data in one or more data storage elements 107 of the memory cells 104. During each read and write cycle, the R/W control module may access a given memory cell 104 by applying a voltage to a local word line 118 of a block 116 in the memory array 102. During a read cycle, the sense amplifiers 110 may detect the presence or absence of data in a given data storage element 107 of a memory cell 104 in communication with a local word line 118. During a write cycle, the bit line decoders 109 may select a given memory cell 104 for storing data.
For example, as shown in FIG. 2B, local word line 118-1,Q is active. In other words, the word line driver 108-Q may apply a voltage to local word line 118-1,Q. Multiplexers 122-1,Q 122-2,Q . . . , and 122-L,Q may select local bit lines 120-1,1,Q, 120-1,2,Q . . . , and 120-1,L,Q for reading and writing operations. Thus, memory cells 104-1,1, 104-1,2, . . . , and 104-1,L may be conducting. To read data, the sense amplifiers 110 may detect the presence or absence of data in the memory cells 104 in communication with the selected local word line 118 and the selected local bit lines 120. In the configuration shown in FIG. 2B, L memory cells 104 may be read during a read cycle. To write data, the bit line decoder 109 may select memory cells 104 for storing data via global bit lines 114 and multiplexers 122.